Ion implanters can be used to treat silicon wafers by bombardment of the wafers with an ion beam. One use of such beam treatment is to selectively dope the wafers with impurities of controlled concentration to yield a semiconductor material during fabrication of a integrated circuits.
A typical ion implanter includes an ion source, an ion extraction device, a mass analysis device, a beam transport device and a wafer processing device. The ion source generates ions of desired atomic or molecular dopant species. These ions are extracted from the source by an extraction system, typically a set of electrodes that energize and direct the flow of ions from the source. The desired ions are separated from byproducts of the ion source in a mass analysis device, typically a magnetic dipole performing mass dispersion of the extracted ion beam. The beam transport device, typically a vacuum system containing an optical train of focusing devices transports the ion beam to the wafer processing device while maintaining desired optical properties of the ion beam. Finally, semiconductor wafers are implanted in the wafer processing device.
Batch ion implanters include a spinning disk support for moving multiple silicon wafers through the ion beam. The ion beam impacts the wafer surface as the support rotates the wafers through the ion beam.
Serial implanters treat one wafer at a time. The wafers are supported in a cassette and are withdrawn one at time and placed on a support. The wafer is then oriented in an implantation orientation so that the ion beam strikes the single wafer. These serial implanters use beam shaping electronics to deflect the beam from its initial trajectory and often are used in conjunction with co-ordinated wafer support movements to selectively dope or treat the entire wafer surface.
Ion sources that generate the ion beams used in existing implanters are typically so called arc ion sources and can include heated filament cathodes for creating ions that are shaped into an appropriate ion beam for wafer treatment. U.S. Pat. No. 5,497,006 to Sferlazzo et al concerns an ion source having a cathode supported by a base and positioned with respect to a gas confinement chamber for ejecting ionizing electrons into the gas confinement chamber. The cathode of the '006 patent is a tubular conductive body and endcap that partially extends into the gas confinement chamber. A filament is supported within the tubular body and emits electrons that heat the endcap through electron bombardment, thermionically emitting the ionizing electrons into the gas confinement chamber.
U.S. Pat. No. 5,763,890 to Cloutier et al also discloses an arc ion source for use in an ion implanter. The ion source includes a gas confinement chamber having conductive chamber walls that bound a gass ionization zone. The gas confinement chamber includes an exit opening to allow ions to exit the chamber. A base positions the gas confinement chamber relative to structure for forming an ion beam from ions exiting the gas confinement chamber.
Other sources may drive RF, microwave or electron beam discharges to generate desired ions. These sources generate plasma densities 10-100 times lower than arc ion sources and are typically used with source materials that have low ionization potentials (species that are easy to ionize) or when the source chamber includes large ion extraction areas. While cold ion sources such as shown in U.S. Pat. No. 6,975,072 to Leung et al can have source materials made of relatively low temperature materials such as stainless steel, copper or aluminum, hot sources like arc ion sources expose the source chamber walls to an arc plasma of temperature of several tens of thousands of degrees Celsius and high thermal power densities which have required source components of prior art implanters to be made of high temperature, so called refractory, materials, such as molybdenum, tantalum or tungsten. See also the article “Water Cooled Plasma Flood Source for Intense Ion Beam Implantation” to Zhimin Wan et al IEEE, 2002 and US published application 2003:0218429.